The present invention relates to a power transmission unit for motor vehicles, and more particularly to self-lubrication means for a differential gear unit of the transmission unit.
In a power transmission unit which comprises a final drive gearing having a drive pinion shaft journalled along the fore-and-aft axis of the vehicle on an upright lateral partition wall of a trans-axle casing, a crown wheel is assembled integral with a differential gear unit in a front chamber formed by the partition wall and is rotated by meshing engagement with a drive pinion integral with the drive pinion shaft to drive the differential gear unit. The differential gear unit is provided with a pair of side-journals which are rotatably supported by a pair of spaced bearings carried on the trans-axle casing, and a pair of wheel axles extending outwardly from the differential gear unit through the side-journals are surrounded by a pair of seal members carried on the trans-axle casing to retain lubricating oil within the front chamber. In operation of the transmission unit, lubricating oil picked up by rotation of the crown wheel serves to lubricate each side-journal of the differential gear unit and each sealed portion of the wheel axles surrounded by the seal members. It is, however, observed that sufficient lubricating oil may not be supplied to the side-journals and the sealed portions of the wheel axles because the picked up lubricating oil flows mainly around the crown wheel. This results in undesired frictional defacements of the side-journals of the differential gear unit and the seal members.